Potterton fault code E321, which may also appear as 163, is listed by Baxi as a domestic-hot-water NTC sensor fault for the Potterton Assure Combi and System group. The official table contains entries for both a short-circuit and an open-circuit condition.
That means E321 identifies a problem with the hot-water temperature-sensing circuit, but the display alone does not tell a homeowner whether the sensor, wiring, connection or control is responsible.
What does Potterton E321 or 163 mean?
An NTC sensor is used by the boiler controls to monitor temperature. Its electrical behaviour changes with temperature, allowing the boiler to regulate hot water. If the signal is outside what the controls expect, the boiler can stop or limit operation.
Baxi’s public table lists E321 / 163 twice: once for a domestic-hot-water NTC sensor short circuit and once for an open circuit. Both require internal checks; neither should be interpreted as a homeowner repair instruction.
Which Potterton boilers use E321?
The current Baxi code group includes Potterton Assure Combi and Potterton Assure System boilers. Other Potterton ranges can use different codes, sensors and control systems.
Check the complete model name on the casing or paperwork. If your boiler is not an Assure model, use the manual for that exact appliance rather than assuming E321 has the same meaning.
What symptoms might accompany the code?
Hot water may be unavailable, may run at an unexpected temperature or the boiler may lock out. Symptoms alone cannot identify the failed part because the controls rely on several connected elements.
On a system boiler, hot-water arrangements also involve external components and a cylinder. The engineer will consider the complete installation as well as the displayed code.
Safe things to record
- Photograph the complete display and any symbols.
- Note whether E321, 163 or both appear.
- Confirm whether the boiler is an Assure Combi or Assure System.
- Record whether central heating still works.
- Note whether hot water is cold, intermittent or unusually hot.
- Write down whether the fault started after a power interruption or recent work.
If the exact user guide permits a reset, one reset may be tried. Stop if E321 returns. Repeated resets do not repair a sensor circuit and can remove useful information about when the fault occurs.
What should you not do?
Do not remove the boiler casing, test sensor resistance, disconnect wiring or bridge electrical connections. Do not buy a replacement sensor solely from the code.
Although NTC sensor faults are often discussed online as simple part changes, the circuit must be checked safely and the correct model-specific component identified.
What happens during a repair?
The engineer will confirm the model, code and stored fault history, then assess how the boiler responds to a hot-water demand. Appropriate checks can be made to the temperature-sensing circuit, its connections and the controls.
The repair depends on measured results. A sensor may be involved, but wiring, connectors or control components should not be ruled in or out without testing.
Is the water safe to use?
If the boiler is producing water at an unpredictable temperature, stop using that outlet until the problem is resolved, particularly where children or vulnerable people could be scalded. Do not rely on mixing cold water to manage a boiler that is behaving abnormally.
Can heating still work?
It may, depending on the model and fault state, but normal heating operation does not mean the hot-water sensor fault is repaired. Record whether heating and hot water are affected separately.
When is urgent action needed?
Switch the appliance off and arrange prompt attention if water becomes dangerously hot or there is leaking water near electrics. If you smell gas or suspect carbon monoxide, move to fresh air and call 0800 111 999.
What helps when booking?
Send a photo of the code, the full Potterton model and a description of the hot-water behaviour. Include whether heating works and whether any work or power interruption preceded the fault.
If your boiler shows a dry-fire warning instead, see our Potterton E270 guide.
Get your Potterton hot-water fault fixed.
Choose a fixed-price boiler repair so the E321 fault can be checked properly and the correct repair completed.
Potterton E321 FAQs
Are E321 and 163 the same code?
For the applicable Potterton Assure models, Baxi pairs E321 / 163 with domestic-hot-water NTC sensor circuit faults.
Does E321 prove the sensor has failed?
No. The sensor circuit, wiring, connections and controls may need checking before a part is selected.
Can I test the sensor myself?
No. That requires internal electrical work. Keep the casing closed.
Should I keep resetting it?
No. Follow the exact guide once if appropriate, but arrange a repair if E321 returns.